1. Field of the Invention
The present invention relates to a color liquid-crystal display device, and, in particular, to a liquid-crystal display device which is superior as a portable device and uses a plastic-film substrate.
2. Description of the Related Art
Liquid-crystal display devices have been used in various fields. As an information display device, a liquid-crystal display device is a match for a CRT. In particular, in a portable apparatus, it is demanded that a size of the apparatus be small, a weight of the apparatus be light, and power consumption of the apparatus be low. Therefore, a liquid-crystal display device is used in such a portable apparatus in many cases. In almost all cases, a liquid-crystal display device uses a glass as a substrate. However, in a portable apparatus such as a portable telephone, an electronic pocket book or the like, a liquid-crystal display device using a plastic film as a substrate is used. A plastic film has a thickness on the order of 0.1 through 0.3 mm, and the weight thereof is light. Therefore, a plastic film is suitable for being used in a portable apparatus. However, performing fine patterning on a plastic-film substrate is difficult. Further, the dimensions of a plastic-film substrate change due to environmental changes in temperature, humidity and so forth. Therefore, it is difficult to put a color filter using a plastic-film substrate into practice. As a result, in almost all cases, a plastic-film substrate is used in a monochrome display device. A color displaying method which does not use a color filter using a plastic-film substrate has been proposed. However, in this method, the number of colors which can be displayed is limited, and displayed colors are not clear. Further, in this method, it is necessary to strictly control a distance (cell gap) between two substrates. Because control of the distance between two substrates is difficult in a plastic-film liquid-crystal display device, this method has yet to be put into practice.
As methods for manufacturing a color filter for a liquid crystal, various methods such as a dye dissolution method, a pigment dispersed method, an electro-deposition method, a micelle-disruption method, a printing method and so forth have been proposed. (With regard to the micelle-disruption method, see `Formation of Organic Thin Films by Electrolysis of Surfactants with the Ferrocenyl Moiety`, Tetsuo Saji, Katsuyosi Hoshino, Yoshiyuki Ishii, and Masayuki Goto, J. Am. Chem. Soc. 1991, 113, 450-456.) In each of the dye dissolution method, pigment dispersed method, printing method and so forth, in forming patterns of red (R), green (G), blue (B) and black (BK), it is necessary to accurately positioning each pattern with respect to the other patterns. For example, first, a black pattern is formed, and, then, red, green and blue patterns are accurately positioned with respect to the black pattern and are thus formed. Further, positioning between the color filter patterns and liquid-crystal driving electrodes is also necessary. An accuracy in positioning depends on material, size, and manufacturing apparatus for a substrate to be used. When a glass substrate is used, it is possible to perform positioning on the order of microns. In comparison to the glass substrate, a plastic substrate changes in dimensions greatly. Not only due to thermal hysteresis but also due to temperature and humidity changes, a plastic substrate changes in dimensions by .+-.0.1%. Therefore, it is very difficult to perform accurate positioning of color filter patterns. In order to put forming of color filter patterns on a plastic-film substrate into practice, a manufacturing process, which does not need accurate positioning of color filter patterns, or, in which the number of steps which needs accurate positioning is reduced to the utmost, is demanded.
In each of the electro-deposition method and micelle-disruption method of the above-mentioned methods for manufacturing color filters, color filter layers are formed on transparent conductive film patterns electrochemically. Therefore, deviation in positions of the respective colors, R, G, B, with respect to each other does not occur.
Japanese Laid-Open Patent Application No. 6-34809 discloses using electrodes for driving liquid crystal also as electrodes by which color filter layers are formed, as a result of making the color filter layers of conductive material or mixing conductive material in the color filter layers.
When the color filter layers are conductive, when a plurality of colors (for example, three colors, R, G, B) of color filter layers are formed, it is necessary to selectively connect the electrodes to an external circuit for each color. Generally speaking, the pitch of the electrodes is equal to or less than 100 .mu.m. It is difficult to directly probe each electrode so as to connect the electrode to an external circuit. Therefore, in the art disclosed in Japanese Laid-Open Patent Application No. 3-102302, as shown in FIG. 1, electrode connecting holes 2 are formed in a photosensitive resin 3 so that electrodes 1 for the respective colors R, G, B on a substrate 4 can be selectively connected to an external circuit. Then, as shown in FIG. 2, the electrodes 1 are selectively connected to the external circuit 7 through conductive silver paste 6. Then, a color filter forming area 5 is immersed in electrolytic liquid, and a voltage is applied to the electrodes selectively connected to the external circuit 7. As a result, color filter layers 8 are formed on the electrodes 1, respectively. However, when attempting to form conductive color filter layers on a plastic film in this method, problems such as shifting of the electrode connecting holes 2 from the electrodes 1, poor electrical connection between the electrodes 1 and the silver paste 6, and so forth, due to change in dimensions of the substrate 4, occurred. As a result, good conductive color filter layers could not be formed.
Further, Japanese Laid-Open Patent Application Nos. 2-175897 and 3-4202 disclose methods in which electrode connecting holes 2 are not used, and, electrodes after being colored are cut by etching. However, in either method, manufacturing steps are complicated, and it is difficult to apply the method to a plastic film substrate.